It hasn't been long since Overwatch's Mercy received a major rework, but Blizzard is apparently pushing ahead with a nerf for her character in the newest PTR.
In the new PTR, Mercy's Valkyrie ability no longer resets or lowers the cooldown of her Resurrect ability. Previously, whenever Mercy went into Valkyrie mode, the cooldown on her Resurrect ability dropped from 30 seconds to 10 seconds, which let her quickly Resurrect multiple characters. That's no longer the case now in the PTR. Instead her Resurrection cooldown remains at 30 seconds while her Resurrect's maximum range has been doubled.
Both Mercy and D.Va received significant changes in the last Overwatch patch to help better balance each character. For Mercy, her ultimate ability "Resurrect" was changed into "Valkyrie" which allowed her to gain an increase in damage output and the ability to fly. Meanwhile here trademark Resurrect move became a regular skill, with a 30-second cooldown and could only be used on a single character instead of a whole area.
The change basically made Mercy one of the most powerful support characters in the game. Maybe too powerful, which is why Blizzard is experimenting with Mercy a bit more in the current PTR.
The new Mercy nerf is available to test out now in the Overwatch PTR on PC.